01Principles and purposeThe professional or clinical skill and the decisions it supports.
Capacity is the ability to make a particular decision, not a global label attached to a person. Complexity and consequences affect what information is relevant, but the assessor must not raise the threshold because they dislike the choice. The practical sequence is to define the decision, presume capacity, identify a reason for doubt, provide support, apply the jurisdiction’s test, record the causal link and then use the correct decision-making authority if capacity is lacking.
For England and Wales, the Mental Capacity Act 2005 applies from age 16. Sections 2 and 3 require both an impairment or disturbance in the functioning of mind or brain and resulting inability to make the decision. Section 4 supplies a best-interests checklist rather than permission to choose what professionals prefer. Scotland’s statute uses benefit, least restriction, present and past wishes and consultation. Current Northern Ireland provisions must be checked because only phases of the Mental Capacity Act (Northern Ireland) 2016 are commenced.
Key points
- Capacity is decision-specific and time-specific. Define the exact decision before assessing; a diagnosis, cognitive score, detention status or previous finding cannot answer the question by itself.
- Presume capacity and take practicable steps to support decision making: treat reversible factors, optimise timing, adapt communication, use an interpreter or communication aid, and reduce avoidable pressure.
- In England and Wales, apply the Mental Capacity Act 2005 diagnostic and functional test: an impairment or disturbance must make the person unable to understand, retain, use or weigh relevant information, or communicate the decision.
- The burden is on showing lack of capacity on the balance of probabilities. A decision others regard as unwise is not enough, and short retention may be sufficient for the immediate choice.
- If capacity is absent, identify any valid and applicable advance decision or authorised decision-maker, then determine best interests using wishes, feelings, beliefs, values, consultation and the least restrictive effective option.
- Jurisdiction matters: Scotland uses the Adults with Incapacity (Scotland) Act 2000 and its benefit framework; Northern Ireland’s 2016 Act is only partially commenced, so check the live local framework and code.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Delirium, intoxication, severe pain, brain injury, cognitive disorder, psychosis, communication difficulty or marked inconsistency may justify assessment. Begin with evidence related to the actual choice; do not perform blanket capacity testing because a person is old, disabled or detained.
Fluctuating attention, hypoxia, medication effects, fatigue, fear, language mismatch or sensory loss can impair performance. Where the decision can wait, correct the barrier and assess at the best time; urgency may require a proportionate decision with the information available.
A person may repeat facts yet be unable to integrate a foreseeable consequence into the choice because of the impairment. Explore reasoning respectfully and distinguish inability from a value judgment, mistrust, denial, risk tolerance or a coherent but unconventional belief.
Relatives may know the person well but do not automatically hold legal authority. Check the scope and validity of any welfare lasting power of attorney, deputyship, Scottish welfare power or advance decision, and seek advice when authority or applicability is disputed.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Decision formulation - Why
- State the choice, available options, timing and foreseeable consequences in concrete terms.
- Interpretation and limitations
- A finding for consent to surgery does not establish capacity for residence, finances or future treatment. Break compound decisions apart and avoid testing abstract knowledge that is not relevant to the choice.
- 02
Support and communication assessment - Why
- Identify adjustments that may enable the person to decide.
- Interpretation and limitations
- Record language, hearing, vision, preferred communication, fatigue, pain, environment and trusted support. A speech impairment does not equal incapacity; any reliable communication method can express a decision.
- 03
Functional interview - Why
- Examine understanding, retention, use or weighing, and communication against the relevant legal test.
- Interpretation and limitations
- Use open questions and ask the person to compare options and consequences. Record answers and the information supplied, showing how any inability results from the impairment rather than merely announcing a conclusion.
- 04
Authority and wishes search - Why
- Find prior decisions and people with a legally defined role if capacity is lacking.
- Interpretation and limitations
- Review accessible records, advance decisions, emergency plans, attorney or court documentation, and consult those close to the person. Verify scope, activation conditions and applicability before treating a document or relative as determinative.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked caseFluctuating delirium and a non-urgent procedureAn older inpatient with infection and fluctuating attention is asked to consent to a procedure that can safely wait until morning; she gives inconsistent accounts of its purpose and risks.+
- 1Define the immediate decision and establish why capacity is in doubt, avoiding any broader conclusion about all decisions.
- 2Optimise decision making by treating delirium contributors, ensuring hearing aids and familiar communication, reducing noise and returning at the patient’s best time.
- 3Explain the options and assess understanding, retention, use or weighing and communication; document the patient’s own responses and the causal link to delirium.
- 4Final action: because delay is safe, defer the procedure and reassess rather than making an immediate substitute decision.
- 5Verification: reassess the same decision when attention improves, record the new findings and obtain consent only if the patient can then decide.
02Structured approachBest interests after capacity is absentA patient lacks capacity for treatment and there is no valid applicable advance refusal or attorney with relevant authority.+
- 1Identify clinical benefits, burdens, uncertainties and the option of no treatment, while avoiding discrimination about age, disability or perceived quality of life.
- 2Ascertain past and present wishes, feelings, beliefs and values from the person, records and people who know them, and involve the person as far as possible.
- 3Consult relevant relatives, advocates and the care team as informants, consider whether capacity may return, and compare less restrictive effective options.
- 4Make and record the best-interests or jurisdiction-specific overall-benefit decision, named decision-maker and review plan; escalate unresolved serious disagreement.
03Escalation approachDisputed high-consequence assessmentThe patient, family and treating team disagree about capacity and the proposed intervention carries major or irreversible consequences.+
- 1Pause non-urgent irreversible action, provide advocacy and obtain senior clinical input from professionals relevant to cognition or communication.
- 2Repeat or jointly review the assessment with clear evidence, separating disagreement about the outcome from the legal capacity question.
- 3Use local mediation and legal advice, and seek a court decision when the law or serious unresolved dispute requires authoritative determination.
- 4Continue necessary care, communication and documentation while avoiding coercion or delay that creates preventable clinical harm.
05Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- Reassess when capacity may fluctuate, reversible factors improve, the decision changes or new information materially alters its consequences; specify the trigger rather than writing “review capacity” without a plan.
- Audit notes for the exact decision, support attempted, relevant information, the person’s responses, statutory criteria, causal link, conclusion and any best-interests process.
- Seek feedback from the patient, advocate and multidisciplinary team about communication adjustments and whether the person had a genuine opportunity to participate.
- For supervised practice evidence, compare an initial and repeat assessment, explaining what changed and why the result reflects time-specific ability rather than professional preference.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Cognitive tests are collateral
A cognitive screening score may identify impairment or inform support but cannot substitute for a decision-specific capacity interview. NICE specifically warns against using a single tool not designed for capacity as the basis of the conclusion.
Retention is proportionate
The person need only retain relevant information long enough to make the decision. Written prompts, repetition and staged conversations can support retention and should be considered before concluding inability.
Advance refusals have conditions
In England and Wales, check validity and applicability; an advance decision refusing life-sustaining treatment has additional formal requirements. An advance request does not compel clinically inappropriate treatment.
Liberty is a separate question
Capacity to consent to care and whether arrangements amount to a deprivation of liberty are related but distinct legal questions. Use the current jurisdiction-specific authorisation route and seek specialist advice.
07Common pitfallsFrequent interpretation and management errors.
- 01
Writing “lacks capacity due to dementia” without defining the decision, testing functional abilities or showing how the impairment causes the inability.
- 02
Using a relative’s agreement as substitute consent without checking legal authority and the proper best-interests or benefit process.
- 03
Testing capacity during avoidable pain, fatigue or communication failure and omitting practicable support that could enable the person to decide.
- 04
Treating an unwise choice, inconsistent lifestyle or refusal of medical advice as proof that the person cannot use or weigh information.